Electrical fire preventing system for aircraft



A. MATHISEN 2,385,825

ELECTRICAL FIRE PREVENTING SYSTEM FOR AIRCRAFT Oct. 2, 1945.

Filed May 15, 1943 4 SheetsSheet l Oct 2, 1945. MATHlSEN 2,385,825

ELECTRICAL FIRE PREVENTING SYSTEM FOR AIRCRAFT Filed May 15, 1943 4SheetsSheet 2 O V O o i T m (i Q 2 2o- Inventor A/VDERS MA ru/ss/v,

A Home y Oct. 2, 1945. A. MATHISEN ELECTRICAL FIRE PREVENTING SYSTEM FORAIRCRAFT 4' Sheets-Sheet 5 Filed May 15, 1943 U yR- A tlorney Oct. 2,1945.

Filed May 15, 1945 A. MATHISEN ELECTRICAL FIRE PREVENTING SYSTEM FORAIRCRAFT 4 Sheets-Sheet 4 A Home y 'tofore known has provide asatisfactory means for reducing fire "Patented Oct. 2, 1945 ELECTRICALFIRE PREVEN TIN G SYSTEM FOR AIRCRAFT Anders Mathisen,

Isleworth, England, assignor to Gravlner Manufacturing Company Limited,Isleworth, Middlesex, England 1943, Serial No. 487,176 In Great BritainJuly 8, 1942 Application May 15 11 Claims.

This invention relates to certain new and usefulimprovements upon ormodifications in electrically actuated fire preventing and fireextinguishing systems.

Extensive use of such described systems hereproved that these in generalrisks upon aircraft but experience has shown that electrical equipmentand especially the cables upon the aircraft may be damaged or fracturedin aircraft crashes, and the principal object of the present inventionis to provide a firefighting equipment for aircraft comprising anelectric circuit cut-out switch incorporating contact members ofsubstantial current carrying capacity, which members are adapted to beclosed under substantial pressure, means being provided for opening saidcontacts when abnormal deceleration is applied to the aircraft, suchopening however being arranged to take place after a slight time lagbetween the application of deceleration to the aircraft and the openingof said contacts, for the purpose of ensuring that fire extinguishersand other types of equipment, which require electric current foroperation under crash conditions, are effectively operated be fore theelectric current supply is disconnected.

The cut-out switch is provided with means for closing the contactmembers, said means being in the nature of a solid abutment which isadapted to apply substantial pressure to the contact members of thecut-out switch in order to ensure high current carryingcapacity of saidcontacts.

The means for effecting opening of said contact members of the cut-outswitch is preferably in the form of an explosive charge adapted todisplace said abutment when the charge is ignited by electrical means.

The means for effecting opening of the cut-out switch preferablycomprises an inertia element operated electric switch adapted to effectignition of said explosive charge when abnormal deceleration is appliedto the aircraft.

One object of the present invention is to ensure continued operation ofelectric equipment upon aircraft such as electric ignition devices, andelectrically automatically operated fire extinguishers and otherelectrical apparatus, during the period between the application ofabnormal deceleration to the aircraft and the opening of said cut-outswitch, and to this end a slight time lag is introduced in the operationof said switch, and while any type of time lag device may be used, apreferred method of obtaining a prolonged time lag of the order of fromfive to ten seconds is by the introduction of a liquid-containingdash-pot device which when incorporated in said cut-out switchmechanism, is adapted to permit retarded movement of a contact actuatingmember normally forced by said abutment into contact with bridge membersof the contact arrangement of the cut-out switch, resilient means suchas springs being interposed between said actuating member and thecontact bridge members to permit relative movement therebetween, wherebythe contact bridges are retained in contact with the contact studs ofthe device for a predetermined period, after ignition of the explosivecharge, and consequent instantaneous removal of the abutment. I

An alternative method of introducing a time lag of the order of from oneto two or three seconds is by the employment of a slow-burningelectrically ignited fuse device which ignites the explosive chargeafter the requisite time lag following ignition due to operation of theinertia element operated switch.

The cut-out switch comprises two pairs of contact studs the first pairbeing adapted for connection to the current carrying cables from astorage battery as normally used upon aircraft, the other pair ofcontact studs being connected to the cables extending to the electricalequipment of the aircraft, usually drawing heavy currents such as motorstarters and various heating equipment.

The studs connected to the individual cables from the storage batteryand the cables extending to the electrical equipment on the aircraft areadapted to be bridged by bridge members of substantial section, whichbridge members are mounted upon an insulating actuator having springmeans associated therewith which normally tend to move said actuatoraway from the contact studs, said insulating actuator also beingprovided with means for engagement with a solid material abutment of thedevice so as to force said bridge members into contact with said contactstuds against the action of the spring normally tending to open thecut-out device.

According to a further feature of the invention, fire-fighting equipmentfor aircraft as described above incorporates one or more electricallyactuated fire extinguisher fluid containers associated with each engine,an inertia element operated switch device being provided for effectingdischarge of said containers over the engines under crash conditions,fire-responsive switch means being furthermore provided for effectingdischarge of said containers when a fire occurs on one of the saidengines, manual switch control means being also provided for effectingdischarge of said containers when desired by air; craft crew members.

Further objects and features of the invention will appear from thefollowing description of the invention with reference to theaccompanying drawings in which embodiments of the invention are shown byway of example and in which- Figure 1 shows fire-fighting equipment uponan aircraft.

Figure 2 shows one form of cut-out switch in vertical section, themechanism being shown i the normal circuit closing position.

Figure'3 shows a side view of Figure 2 in partial section, the mechanismbeing shown in the circuit opening position.

Figure 4 is a sectional plan view taken on line l-l of Figure 2.

Figure 5 is a base view of the cut-out switch viewed from below Figure3.

V Figure 6 is a view corresponding to Figure 2 and showing a modifiedform of mechanism, and

Figure 7 is a. partial sectional view of a further modification of partof the device shown in Figure 2.

Similar letters and numerals of reference relate to like parts in allthe figures of the drawings.

In Figures 1, a denotes the fuselage of an aircraft and b the wings andc the engine nacelles. d denotes a radial cylinder engine of thedowndraught carburettor type having an air intake denoted e.

The fire-fighting equipment comprises fire extinguisher liquidcontainers A and B associated with the engine d, and extinguishers C andD v are associated with fuel tanks f and g.

Extinguisher A has a plain pipe portion F extending to a spray nozzle Gon air intake e, and from this connects further to a horizontal loop ofperforated spray piping which encircles the carburettor system, the pipebeing then bent into a vertical loop encircling the aero engineaccessory parts so as to spray these parts with fire extinguishingliquid when extinguisher A is discharged.

- Fire extinguisher B has a plain pipe portion H extending fromextinguisher B to the engine mounting plate, the perforated pipe portionthen encircling the crank case of the engine at the rear of thecylinders, the pipe then extending between the lower cylinders toencircle the crank casing in front of the cylinders. 1

Extinguisher C has a perforated pipe I extending therefrom to encirclefuel tank I, and extinguisher D has a perforated pipe J extendingtherefrom to encirclefuel tank g.

The various extinguishers are controlled by a plurality of automatic andmanually operated switches including inertia element operated A cabletype or flame detecting element N is associated with extinguishers A andB which element will effect discharge of these extinguishers if a fireoccurs on the aero engine.

Flame detecting switches O are associated with fuel tanks 1 and g whichswitches when ignited by ,fiame from burning escaping fuel will effectdischarge of extinguishers C or D associated with the tank on fire.

The fire-fighting equipment is electrically ener gised from the aircraftstorage battery i which has the conducting leads connected to automaticcut-out switch P further hereinafter described in detail.

The storage battery leads extend from the cutout switch P to amulti-terminal block or distributor panel i, the circuit arrangementsbeing such that electric current from the storage battery through theelectrically ignited fire extinguisher discharge heads is passed uponclosure of any one of the various controlling switches to eflectdischarge of the extinguisher in the part of the aircraft on fire.

The fire-fighting equipment disclosed in Figure 1 isthat associated withthe starboard wing of the aircraft, but it will be understood of coursethat identical equipment is provided in the port wing, which is howevernot being shown for the sake of clearness.

Referring to Figures 2, 3, 4 and 5 which show the construction ofautomatic cut-out switch P, numeral 2 denotes a contact stud ofsubstantial section faced with a soft high-conductivity disc 3 (Fig. 3)brazed or similarly secured thereto, said stud being provided with alocknut 4 and a securing nut 5 whichis adapted to secure a cable lugextending from the aircraft storage battery to said stud. Fig. 2 showsthecut-out switch in normal unactuated position with contacts v closed,and Fig. 3 shows the cut-out switch in actuated position with contactsopen.

Numeral 6 denotes a second stud provided with disc I and nuts 8 and 9 towhich stud a lug secured to the cable a: (Fig. 1) extending to theaircraft electrical equipment requiring large currents is secured.

Studs 2 and 6 (Fig. 3) are mounted in an insulating base l0, said basebeing provided with spacing lugs Ii adapted to reduce risk of electricalcontact between the adjacent studs, and

, said base carries an additional pair of studs I2 switch K which ismounted in a forward posi- Y tion in the fuselage on transverse fuselagestructure frame member h below the floor and adjacent the skin of theaircraft, so that impacts will be imparted to switch K when an aircraftmakes a belly landing. Switch K effects dis-' charge of allextinguishers A, B, .C and D in a crash.

Gravity operated switch L is also provided for effecting discharge ofall the extinguishers when an aircraft turns over on its back.

Pilot-operated push button switch M is provided in the pilot'scompartment'for effecting discharge of extinguishers A and B if anengine is found to be on fire.

and i3 fitted with securing nuts I4 and I5, whereto the second cablefrom the accumulator and the corresponding cable 1 (Fig. 1) extending tothe heavy current electrical equipment of the aircraft are connected.

Studs 2, U and l2, l3 are bridged by a pair of displaceabiy mountedbridge members it and ll, of substantial current carrying capacity, saidmembers being also provided with soft high conductivity discs I! and i9brazed or otherwise secured thereto.

Bridge members I6 and i1 are provided with guide and actuating studs 20and 2| which are engaged by a transverse insulating actuator 22 which isprovided with a strut member 23 adapted to engage a solid materialabutment 24 which is integral with a similar material screwed fitting25, said abutment being screw-threaded and provided with a nut 26adapted to confine an explosive charge 21 between said abutment nut andthe walls of fitting 25, so that whenthe charge is ignited by anelectrically ignited fuse device 28 the abutment 24 will be blown awayto permit upward movement of strut 23 and assaaas actuator 22, underaction of spring 28, into the position indicated in Figure 3 to open theelectrical connection between studs 2 and 8, I and I3. The mechanicalconnection between abutment 24 and fitting 25 is restricted, so that itis readily'broken by the explosive charge.

Fuse 28 is of a known type and is provided with electrical leads adaptedto be connected to plug-in socket pins 38 with which an appropriateplug-in socketof a knowntype is adapted to engage, said socket beingconnected to the inertia switch and the aircraft storage battery asthrough cable w (Fig. 1) to effect ignition of fuse 28 when the contactsin the inertia switch close.

In order to restrict the movement of abutment 24 and nut 28 afterdisplacement by the explosive charge, a cap 3| is secured to fitting 25,said cap 3| being provided with vanes adapted to reduce the impactwhereby parts. and 28 would otherwise strike the walls of cap 3|.

Springs 32 and 33 are interposed between bridge members l1 and I8 andinsulator actuator 22, the arrangement being such that when abutment 24is blown away actuator 22 commences to move in the upward direction,whereas springs 32 and 33 owing to their expansionretain contact bridgesl8 and IT in contact with studs 2, 8 and I2, I3 for a predetermined timelag.

In the device shown in Figures 2, 3, 4 and 5, the time lag is obtainedby a dash-pot device constituted as an oil containing chamber 34 formedin insulating base l8 into which an extension 35 of strut 23 having avane 38 secured thereto projects so that the vane is submerged in liquidin chamber 34 as indicated in Figure 2.

Vane 38 is provided with a restricted diameter orifice 31 whichregulates the retardation applied by extension 35 and vane 38 to themovement of actuator 22, and chamber 34 is provided with a largediameter portion 38 which permits rapid movement of extension 35 andvane 38 when the vane 38 passes into this portion of the chamber, and bythis means a quick break-action is obtained, between discs 3, I and l8,l9.

As will be seen, the amount of relative movement between bridge piecesl8 and I1 and actu-j ator 22 is restricted by the heads on studs and 2|,as bridges l8 and I! will be moved together with actuator 22 when theseheads rest upon the actuator, the relative amount of displacementobtainable by actuator 22 and bridge pieces l8 and I! being indicated inFigure 3.

As the current carrying capacity of contacts 2, 8, and bridge pieces I8,I1, is required to be of a high order of between 500' and 600 amperes,are reducing means in the form of cup-shaped projections 33 and 48 areprovided from base III as indicated in Figure 3.

In order to obtain satisfactory operation of the device the followingminor constructional expedients are adopted:

Spring 23 is guided in actuator 22 in a recess 4| provided with acentralising spigot 42 in which strut 23 is screwed as indicated inFigure 2.

To prevent loss of fluid from the dash-pot device, a gland cap 43 isscrewed into base I, a liquid-excluding washer 44 being provided at thejoint to prevent leakage of fluid between these parts. Cap 43 isprovided with a gland device comprising gland nut 45 which in additionto compressing packing 48 serves as a centralising spigot for spring 28.

I lag is obtained by Springs 32 and 33 are housed in recesses 4| and 48in actuator 22, andare located by lock-nut devices 43 and 58 securedupon studs 2| and 28.

The above described mechanism parts for the cut-out switch P are housedin an insulation casing 5| secured to base I by screws 52, and in orderto eliminate angular displacement of bridge pieces l8 and I1, saidhousing is provided with guide ribs 53 as indicated in Figure 4, whichfurthermore serve to strengthen the casing.

As will be seen from Figures 2 and 3, fitting 25 is adapted to bescrewed into casing 5| by means of a metal insert 54, and the pressureexerted by abutment 24, strut 23, actuator 22, springs 32 and 33 onbridge pieces l8 and I1, is obtained by screwing fitting 25 into insert54 with the requisite force.

In the modification shown in Figure 6, the time the insertion of a shortlength of fuse cable 55 which when ignited by fuse 28 burns at therateof 1" in 4 seconds, and as the length of fuse cable is approximately4" a time lag of approximately .one second is obtained, which is of theorder required for ensuring operation of fire extinguishers and otheraircraft equipment before the switch contacts open.

In this case the clash-pot device mechanism is omitted but strut 23 isprovided with a guide pin 58 passing through modified gland cap 51'which serves as a guide for pin 58 and as asupport and location forspring 23. I

As will be seen, studs 2| and 28 are shortened and springs 32 and 33 arepermanently in a comparatively highly compressed state, but a slightrelative movement is obtained between actuator 22 and bridge pieces I 8and IT, as the resilient connection between these parts obviates thenecessity for obtaining a high degree of alignment between studs2, 8 and2, l3 and the coeacting bridge pieces I 8 and H.

In the further modification shown in Figure 7, abutment 24 is replacedby a pin 58 which extends from an explosive chamber 59 in a sleeve 88into which a fuse holder 8| containing a delayed action fuse 82 isfitted.

Fuse 82 has electrical leads similar to fuse 28, and these are connectedto a terminal block device 83 to which connections from the inertiaswitch and the accumulator'can be connected,

the fuse 82 being of the delayed action type having a delay period ofbetween 2 and 3 seconds in accordance with requirements.

Fuse holder 8| is provided with a restricted orifice 64 through whichignition of the explosive in the chamber 53 is obtained without risk ofblow-back.

Pin 58 is screwed or otherwise firmly secured in sleeve 88 by screwthreads 85 which serve to locate pin 58 and to obviate risk of loss ofexplosive gases between pin 58 and sleeve 88.

The above parts ar secured in a fitting 88 adapted to be screwedintoinsert 54, said fitting having a recess 81 produced therein intowhich pin 58 can be blown when the explosion takes place,,a verticalrecess 88 being similarly formed in fitting 88 permitting additionaldisplacement of pin 58 and the upward movement of strut 23 as indicatedin dotted lines in Figure '7.

Having thus fully described my invention, what I claim as new and desireto protect by Letters Patent is:

1. Fire-fighting equipment for aircraft comprising one or moreelectrically actuated fire extinguisher fluid containers, an electriccurrent supply source, a load circuit connected to said source, anelectric circuit cut-out switch incorporating electric current carryingcontacts of substantial current-carrying capacity having the contactsconnected in said circuit, means for closing'said contacts undersubstantial pressure, impact operated switch means for effectingdischarge of said containers and for effecting opening of said cut-outcontacts when abnormal deceleration is applied to the aircraft, andmeans for introducing a time lag between the application of decelerationto the aircraft and the opening of said contacts.

2. Fire-fighting equipment for aircraft incorporating one or moreelectrically actuated flre extinguisher fluid containers associated witheach engine, an electric current supply source, flameoperated switchmeans associated with each engine and adapted to effect discharge ofsaid containers when a flre occurs on said engines, an"

electric circuit cut-out switch, and an inertia element operated switchdevice adapted upon application of abnormal deceleration to the aircraftto effect discharge of said containers over said engines under crashconditions and having means for effecting operation of said cut-outswitch after a slight time lag between the application of decelerationto the aircraft and the operation of said cut-out switch.

3. Fire-fightin equipment for aircraft incorporating electricallyactuated fire extinguisher fluid containers associated with the fueltanks, an electric current supply source, flame-operated switch meansassociated with each individual fuel tank adapted to effect discharge ofindividual containers associated with individual fuel tanks when a fireoccurs on said tanks, an electric circuit cut-out switch, and an inertiaelement operated switch device adaptedupon application of abnormaldeceleration to the aircraft to effect discharge of said containers oversaid fuel tanks under crash conditions and having means for effectingoperation of said cut-out switch after a slight time lag between theapplication of deceleration to the aircraft and the operation of saidcutout switch.

4. Fire-fighting equipment for aircraft incorporating one or moreelectrically actuated fire extinguisher fluid containers associated witheach engine and individual flre extinguisher fluid containers associatedwith the aircraft fuel tanks, an eiectric current supply source,flame-operated switch means associated with said engines and with eachindividual fuel tank adapted to effect discharge of individualcontainers associated with said engines and fuel tanks when a flreoccurs on said engines or fuel tanks, an electric circuit cut-outswitch, and an inertia element operated switch device adapted uponapplication of abnormal deceleration to the aircraft to effect dischargeof said containers over said engines and fuel tanks under crashconditions and having means for effecting operation of said cut-outswitch after a slight time lag between the application of decelerationto the aircraft and the operation of said cut-out switch.

5. In fire-fighting equipment according to claim 4, a gravity elementoperated switch adapted to effect discharge of said containers when anaircraft turns over on its back during landing operations.

6. In fire-fighting equipment for aircraft comprising a fire risk,discharge means for delivering fire-extinguishing fluidon said firerisk, a container of fire-extinguishing fluid, electrically actuatablerelease meansv mounted for conan emergency switch serially connected insaid distribution line and being normally adapted to maintain saiddistribution line closed and comprising actuating means actuatable byoperation of said control means for operating said switch to open saiddistribution line, and connections between said distribution line andsaid release means and comprising means actuatable by said control meansfor applying electrical actuating energy to said release means when saidcontrol means is operated.

7. In fire-fighting equipment for aircraft comprising a fire risk,discharge means for delivering fire-extinguishing fluid on said firerisk, a container of fire-extinguishing fluid, electrically actuatablerelease means mounted for controllably connecting said container to saiddischarge means, crash operable control means, a source of electricpower, a distribution line leading from said source to power consumingunits, an emergency switch serially connected in said distribution lineand being normally adapted to maintain said distribution line closed andcomprising actuating means actuatable by operation of said control meansfor operating said switch to open said distribution line, andconnections between said distribution line and said release means andcomprising means actuatable by said control means for applyingelectrical actuating energy to said release means when said controlmeans is operated, said switch further comprising time delay means forappreciably delaying its actuation to open said distribution line afteroperation of said control means.

8. In fire-fighting equipment for aircraft comprising a fire risk,discharge means for delivering fire-extinguishing fluid on said firerisk, a container of fire-extinguishing fluid, electrically actuatablerelease means mounted for controllably connecting said container to saiddischarge means, crash operable control means, a source of electricpower, a distribution line leading from said source to power consumingunits, an emergency switch serially connected in said distribution lineand being normally adapted to maintain said distribution line closed andcomprising actuating means actuatable by operation of said control meansfor operating said switch to open said distribution line, connectionsbetween said distribution line and said release means and comprisingmeans actuatable by said control means for applying electrical actuatingenergy to said release means when said control means is operated, saidswitch further comprising circuit closing and opening movable elements,and two-step time delay means adapted after the operation of saidcontrol means to move said elements in a first step' relatively slowlytoward but not up to circuit opening position and in a second stepstarting just before circuit opening position to move said elementsrelatively rapidly beyond circuit opening position.

9. In fire-fighting equipment for aircraft comprising a fire risk,discharge means for delivering fire-extinguishing fluid on said firerisk, a container of fire-extinguishing fluid, electrically actuatablerelease means mounted for controllably connecting said container to saiddischarge means, crash operable control means, a source of electricpower, a distribution line leading from said source to power consumingunits, an emertion line and being normally adapted to maintain lablyconnecting said container to said discharge means, crash operablecontrol means, a source of electric power, a distribution line leadingfrom said source to power consuming units, an emergency switch seriallyconnected in said distribu-- tion line and being normally adapted tomaintain said distribution line closed and comprising actuating meansactuatable by operation of said control means for operating said switchto open said distribution line, said control means being a crashoperable switch, and connections between said control means, saiddistribution line and said release means, for applying electricalactuating energy to said release means when said control means isoperated, said actuating means for said switch comprising anelectrically fused explosive element connected to said control means forexplosion by operation thereof.

11. In fire-fighting equipment for aircraft comprising a fire risk,discharge means for delivering fire-extinguishing fluid on said firerisk, a container of fire-extinguishing fluid, electrically actuatablerelease means mounted for controllably connecting said container to saiddischarge means, crash operable control means, a source of electricpower, a distribution line leading from said source to power consumingunits, an emergency switch serially connected in said distribution lineand being normally adapted to maintain said distribution line closed andcomprising actuating means actuatable by operation of said control meansfor operating said switch to open said distribution line, said controlmeans being a crash operable switch, and connections between saidcontrol means, said distribution line and said release means, forapplying electrical actuating energy to said release means when saidcontrol means is operated, said actuating means for said switchcomprising an explosive element and an electrically actuatableslow-burning fuse attached to said explosive element and connected tosaid control means for ignition by operation thereof.

ANDERS MATHIBEN.

